SSL Option is not shown at Edit Virtual Server > Enabled features

Hi there, These days I was trying to get SSL certificate to enable HTTPS in all my virtual servers, however I could only manage to do so in my webmin domain (actually it was pretty straight forward using Request Certificate at Webmin Configuration> SSL Encryption> Let's Encrypt option).

Reading a lot of other topics here at the forum I couldn't do the same with my Virtualmin's Virtual Servers... SSL Option is not shown at Edit Virtual Server > Enabled features.

I already checked at Virtualmin> System Settings> Account Plans (there is only 1 plan) > Allowed virtual server features the option "SSL website".

I also am logging as root and not as a virtualmin user.

I only have 1 public IP.
OS: Ubuntu Linux 16.04.3
Webmin version 1.900
Virtualmin version 6.06-2
Usermin version 1.751

Where else should I try looking? Thanks